1. Field of the Invention
The present invention relates to monocomponent and two-component type developer for electrophotography to be used in electrophotographic copying apparatus and printers.
2. Description of the Related Art
Images are produced by electrophotographic copying apparatus and printers by first charging the surface of an electrostatic latent image bearing member, e.g., photosensitive member, with a uniform electric charge, exposing said surface to an exposure light pattern corresponding to the image of an original document, or writing on said surface with light having an output content, so as to thereby form an electrostatic latent image on said surface of the photosensitive member. The surface of the photosensitive member having the aforesaid electrostatic latent image is developed (rendered visible) by a developing device, and the developed toner image is then transferred onto a transfer medium.
The aforesaid developing device uses a monocomponent developing material comprising only a toner, or a two-component developing material comprising a toner and a magnetic carrier to develop the electrostatic latent image formed on the surface of the photosensitive member by uniformly contacting the surface of said photosensitive member. The toner in the aforesaid developing material normally comprises thermoset resin, coloring material, charge-controlling agent, and fluidizing agent and the like. The aforementioned two-component developing material comprises a toner and a magnetic carrier such as ferrite and the like.
Electrophotographic processes using the aforesaid developing materials have in recent years come to require high quality image production. A high degree of uniformity in the density of the solid portion of images is demanded in forming high quality images, such that excellent fluidity is required of the developing material and particularly the toner. Furthermore, improvement of image quality such as in image resolution, tone, or line reproducibility requires toner particles of very small particle diameter. However, as toner particle size becomes smaller, there is a corresponding reduction in toner fluidity which adversely affects developing material transportability, mixing characteristics and the like.
In order to eliminate the aforesaid disadvantages and improve fluidity, blocking resistance and the like, fluidizing agents are added. Fluidizing agents added to the toner use fine particles such as, for example, colloidal silica, titanium oxide, alumina and the like having a mean particle diameter of 10.about.30 nm. The necessity of adding the aforesaid fine particle becomes greater in correlation with the smaller particle diameter of the toner and carrier. However, when a large amount of a fluidizing agent is used, said fluidizing agent is dispersed to the developing apparatus during developing so as to cause toner fogging and soiling of the interior of the image forming apparatus. Furthermore, when a nonmagnetic toner is used, dispersion of the toner itself outside the developing apparatus becomes prevalent.